Go Back  Offshoreonly.com > Technical > General Q & A
98 454 Mag Mpi mid range missfire >

98 454 Mag Mpi mid range missfire

Like Tree5Likes

98 454 Mag Mpi mid range missfire

Reply

Old 05-06-2019, 08:26 PM
  #1
Registered
Thread Starter
 
Join Date: May 2019
Posts: 24
Default 98 454 Mag Mpi mid range missfire

Alright Iíve been reading on this forum for a while trying to figure out this problem.
just bought the boat from original owner 360 hours well maintained.
says he had the dealer do bigger injectors and other work new.
Boat idles great as soon as you get it around 1,000 rpms you can hear it breaking up, hold it wide open and after about 45 seconds it takes off like a bandit up to 4,000 rpms wonít go over. If you hold it mid throttle it rolls coal like a freightliner!
i did plugs cap rotor
changed fuel separator.
checked codes on engine none just flashes 12, watched 4 sets of 12 flash 3 times.
Also boat is a 260 Velocity
any suggestions or help is appreciated.
Sean400 is offline  
Reply With Quote
Old 05-06-2019, 08:52 PM
  #2
SB
Registered
iTrader: (1)
 
Join Date: Nov 2004
Location: On A Dirt Floor
Posts: 9,929
Default

Originally Posted by Sean400 View Post
says he had the dealer do bigger injectors and other work new.
What ? and What ! and What.
SB is offline  
Reply With Quote
Old 05-06-2019, 09:41 PM
  #3
Registered
Thread Starter
 
Join Date: May 2019
Posts: 24
Default

I assume larger injectors cam, roller rockers. From looking into the valve covers I can see crane cam rockers.
Sean400 is offline  
Reply With Quote
Old 05-06-2019, 11:15 PM
  #4
BUP
Registered
iTrader: (8)
 
Join Date: Jul 2011
Location: Ft. Worth TX
Posts: 8,955
Default

you can not just throw larger injectors nor any injectors at it and leave the stock ecm and other internals of the engine. What is your fuel pressure ? what ms pulse width thru out the rpm range is the injectors showing ? You need a scan tool for real diagnostics,

my guess it is the injectors and fuel pressure

So what injectors are installed and the rating of those injectors ?

You need to post your engine serial number as well. Later 1998 was the changing of the big blocks for ecm and a few other systems
BUP is offline  
Reply With Quote
Old 05-07-2019, 05:34 AM
  #5
Registered
 
Join Date: Apr 2019
My Boat: 2007 formula 35 fast tech
Posts: 124
Default

coil?
Nothing personel 353 is offline  
Reply With Quote
Old 05-07-2019, 06:06 AM
  #6
Registered
Thread Starter
 
Join Date: May 2019
Posts: 24
Default

I didnít see The Schrader Valve when peeking around yesterday did see the fuel cooler down by the port side engine mount. What type of scan tool do I need I have obd2 that goes to my laptop but nothing for obd1 or whatever these require. Iíll post serial number when I find it. He told me he had the dealer do the work so I assume the flashes the ecm accordingly along with required parts.
Sean400 is offline  
Reply With Quote
Old 05-07-2019, 06:09 AM
  #7
SB
Registered
iTrader: (1)
 
Join Date: Nov 2004
Location: On A Dirt Floor
Posts: 9,929
Default

You need to find out exactly what was done.All Part #'s , reprogramming,and whom.

No assuming or you could be screwed.

Edit in: Did the engine used to have a Procharger or etc on it ?

Last edited by SB; 05-07-2019 at 06:14 AM.
SB is offline  
Reply With Quote
Old 05-07-2019, 06:54 AM
  #8
Registered
Thread Starter
 
Join Date: May 2019
Posts: 24
Default

It did not have a pro charger
Sean400 is offline  
Reply With Quote
Old 05-07-2019, 08:44 AM
  #9
Registered
iTrader: (3)
 
Join Date: Oct 2007
Location: yorkville,il
My Boat: 31 american offshore,38 fountain fever
Posts: 8,321
Default

my first question is when did this problem start.did it ever run right after the larger injectors were installed.the black smoke makes me think the injectors are causing the problem.
mike tkach is offline  
Reply With Quote
Old 05-07-2019, 08:52 AM
  #10
Registered
Thread Starter
 
Join Date: May 2019
Posts: 24
Default

The injectors were put in when boat was new from dealer. Iíve never had the boat run right no.
Sean400 is offline  
Reply With Quote

OSO Sponsor
OSO Advertiser
OSO Advertiser
OSO Advertiser